## 20.4. Macros

This section summarizes internal macros, modifiers, string substitution, and special macros.

### 20.4.1. Internal Macros

`$?` | The list of prerequisites that have been changed more recently than the current target. Can be used only in normal description file entries--not suffix rules.
`$@` | The name of the current target, except in description file entries for making libraries, where it becomes the library name. Can be used both in normal description file entries and in suffix rules.
`$$@` | The name of the current target. Can be used only to the right of the colon in dependency lines. (May not work on all versions of `make`.)
`$<` | The name of the current prerequisite that has been modified more recently than the current target. Can be used only in suffix rules and in the `.DEFAULT:` entry.
`$*` | The name--without the suffix--of the current prerequisite that has been modified more recently than the current target. Can be used only in suffix rules.
`$%` | The name of the corresponding `.o` file when the current target is a library module. Can be used both in normal description file entries and in suffix rules.

### 20.4.2. Macro Modifiers

Macro modifiers are not available in all variants of `make`.

`D`
  The directory portion of any internal macro name except `$?`. Valid uses are:

  >     $(*D)   $$(@D)
  >     $(<D)   $(%D)
  >     $(@D)

`F`
  The file portion of any internal macro name except `$?`. Valid uses are:

  >     $(*F)   $$(@F)
  >     $(<F)   $(%F)
  >     $(@F)

### 20.4.3. Macro String Substitution

String substitution is not available in all variants of `make`.

`$(``macro``:``s1``=``s2``)`
  Evaluates to the current definition of `$(`macro`)`, after substituting the string s2 for every occurrence of s1 that occurs either immediately before a blank or tab, or at the end of the macro definition.

### 20.4.4. Macros with Special Handling

`MAKEFLAGS` | Contains the flags inherited in the environment variable MAKEFLAGS, plus any command-line options. Used to pass the flags to subsequent invocations of `make`, usually via command lines in a `makefile` that contain `$(MAKE)`.
`SHELL` | Sets the shell that interprets commands. If this macro isn't defined in the description file, the value depends on your system. Some Unix implementations use the shell from the user's environment (as with other macros). Other implementations (including SVR4) set the default `SHELL` to `/bin/sh`.
`VPATH` | (Not available in all variants of `make`.) Specifies a list of directories to search for prerequisites when not found in the current directory.

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